1. Field of the Invention
The present invention generally relates to a network system including a plurality of printers and a printer connected to the network system, and in particular to a power-supply control technique for the printers.
2. Description of the Related Art
In a printer system including a host computer and a plurality of printers which are connected to form a network, the power-supply control of the printers is preformed by the host computer through the network.
For example, there have been proposed a printer power-supply control system which can individually control the power supplies of the network printers through the network and indicate the power-on/off state of each printer (see Japanese Patent Unexamined Publication No. 6-183102). Since the network printers can be powered on and off individually and the power-supply state of each printer can be displayed at the side of a host computer, the network printers may be easily managed by the host computer.
In the network system having a plurality of printers of relatively high power consumption, such as laser printers, however, when a plurality of printers are simultaneously powered on, a large amount of rush current flows, which may cause the circuit breaker to open. Further, since the management processing of the network printers is concentrated on the host computer, each network printer cannot be powered on without starting the host computer.
An object of the present invention is to provide a power-supply control method and a printer system which can prevent a plurality of printers from being simultaneously powered on.
Another object of the present invention is to provide a remote power-supply control method and a printer system allowing easy control operation of the printers in the network system.
Still another object of the present invention is to provide a remote power-supply control method and a printer system allowing efficient control of the printers in the network system.
According to the present invention, the power-supply control of the printers is distributed among the printers.
According to an aspect of the present invention, a main power supply of each of a plurality of printers which are connected to a network is controlled according to the following steps. After assigning priorities to the printers, at each of the printers, an address of another printer having a next-lower priority assigned thereto is stored unless the printer has a lowest priority assigned thereto. When a power-supply control signal has been received, the main power supply thereof is controlled depending on the power-supply control signal and the power-supply control signal is sent to the other printer having the next-lower priority assigned thereto.
The power-supply control signal may be generated at a host computer of the network and then is sent to one of the printers which may be a printer having a highest priority assigned thereto.
Accordingly to another aspect of the present invention, each of the printers stores a first address of a first printer having a highest priority assigned thereto and a second address of a second printer having a next-lower priority assigned thereto. When a power-on request signal has been received, the main power supply thereof is powered on and then the power-on request signal is sent to the second printer having the next-lower priority assigned thereto. When a power switch thereof is switched on, it is determined whether the printer is the first printer and, when the printer is the first printer, then main power supply is powered on and the power-on request signal is sent to the second printer having the next-lower priority assigned thereto. When the printer is not the first printer, the power-on request signal is sent to the first printer having the highest priority assigned thereto.
At each of the printers, preferably, a desired one of a power-on request sending mode and a power-on request non-sending model is selected. When the power-on request non-sending mode is selected, the power-on request signal is not sent in the case where the power switch is switched on.
When the main power supply is powered on, preferably it is determined whether the main power supply thereof is in stable state. When the main power supply thereto is in stable state, the power-supply control signal is sent to the other printer having the next-lower priority assigned thereto.
At a host computer of the network, a priority management table containing addresses of the printers and the respective priorities assigned to the printers is stored. By sequentially selecting the printers, an address of a printer having a next-lower priority than a selected printer is sent to the selected printer. When an acknowledgement is not received from the selected printer within a predetermined time period, an entry of the selected printer may be deleted from the priority management table to update the priority management table.
As described above, according to the present invention, the burdens on the host computer with power-supply control of a plurality of network printers can be reduced.
Further, the printers are sequentially powered on while waiting for power-supply stability according to assigned priorities. Therefore, the printers can be prevented from simultaneously being powered on with reduced burdens on the host computer.
Furthermore, according to the present invention, when any of the printers is manually powered on, the registered printers having lower priorities than the initially powered-on printer are sequentially powered on. Therefore, all the registered printers can be powered on without having to power the highest priority printer on.